A gas fired tangentially boiler was modeled under full load conditions. Furnace was simulated by CFD and then was joint with two mathematical models to calculate heat transfer in the convective section, and metal temperature of waterwall tubes. Effects of changing the combustion excess air (0 to 20%) and burners tilt angle (-30° to +30°) were studied. Results showed that the boiler efficiency is optimum if excess air= 10% and the burners have a negative angle. However, these optimum settings cannot produce a superheated and reheated steam of 538 °C which is desirable. Indeed, a zero or positive tilt angle with 10% excess air, or a negative burner angle with 15% excess air lead to highest efficiency by considering the potential of generating superheated steam of 538 °C. In addition, CO emission in low excess air values growths by increasing the burner tilt angle. NOx emission in low and high excess air ratios is lower at positive burner angles while a moderate excess air (10%) needs a zero tilt angle to minimize NOx emission. Furthermore, a critical fouling thickness was computed, considering boiler's circulation ratio, in which the metal temperature of the waterwall exceeds the short overheating threshold. With a certain thickness of scale layers inside the tubes, a burner tilting equal to 0° or 30° postpones tube rupture. These results could be utilized by operating engineers to keep their utility boilers in the most efficient state and avoiding overheating and tube rupture.

Exergy analysis in power plants is a strong tool to evaluate cycle performance qualitatively. Most of previous studies applied second law approach to find optimum values for main cycle parameters. Although, these researches are useful to improve the design features of future power plants, they do not imply any recommendation to improve an aged unit. In This study an exergy analysis of an operating unit was performed to clear main sources of exergy destruction. Second law efficiency and exergy losses of all main components in the steam power plant, which is located in the south of Iran, were calculated based on present data. To find out aging influence on the plant performance, outcomes were compared with design results. This comparison cleared components which affected by aging, and the amount of miss performance were specified too. Boiler and high pressure turbine (HP) were the most influenced components due to aging effects. Besides, the calculations were done at three loads in order to evaluate performance of components in off design conditions.

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Reduction of fuel consumption in power plants is an important issue due to their high rate of fuel usage. In the present article, this was done by optimizing rotary regenerator which have a great role in recovering thermal energy in power stations. Heat transfer and pressure drop through 13 popular flow passages of power plant's rotary regenerators were obtained by CFD simulations. The outcomes were used in a mathematical model of the rotary air heater by considering air leakages. The model was capable of distinguishing between different heating surfaces. Then it was used for optimizing a regenerator by genetic algorithm. Rotational speed and dimensions of all three layers (hot end, intermediate layer, and cold end) were optimized to achieve the highest fuel saving. These dimensions were: hydraulic diameters, heating profile type, and length of each layer. Results showed that redesigning these parameters to the optimal values leads to saving of 443 kg of natural gas per hour for one regenerator. A 10 meter regenerator also had the highest reduction in fuel consumption (660 kg/hr). Finally, the influence of air and hot gas temperatures, and air mass flow rate on fuel saving and optimum values of design parameters was discussed.

Sugar extraction from sugarcane/sugar-beet is an energy-intensive process, both thermal and electrical energies. However, there are numerous opportunities for energy efficiency improvements. A number of tests were conducted in an old sugarcane factory, including the boiler, electricity generation, process, and mill section, to better understand these opportunities. During four years, specific energy consumption was 16-28 GJ/ton of raw sugar. Measurements and calculations revealed that some equipment, e.g. shredder's steam turbine and some gearboxes, require extensive repairs. The second set of areas for improvement relates to proper operation, such as determining the boiler excess air (which results in an average 0.6% efficiency reduction) and factory planning (near 200 MWh per year). The third type of improvement is to modify or integrate new elements into the existing plant, like water storage tank insulation (3.8 MW) and switching from load-unload operation to drive control for instrumentation compressors (43 MWh). Bangladesh J. Sci. Ind. Res. 58(1), 09-18, 2023